WO 95/27153 describes a known manual clutch, in particular a manual clutch for motor vehicles, that has, in addition to a clutch disc layered with an organic friction lining, a counter rotor and a pressure plate, each of which is layered with a friction lining made up of a powder-metallurgically sintered material. The powder-metallurgically sintered material consists essentially of an iron material that is displaced by an amount of hard particles as friction enhancers and which has in addition a fraction of 10 to 15-weight % copper. A frictional material produced from a powder-metallurgically sintered material has a certain porosity that has a favorable effect on the frictional behavior of the manufactured clutch. Furthermore, it has been shown that the porosity existent on the essentially metallic frictional surface does not deteriorate so easily as the organic friction lining wears down. In addition to being able to removably attach the manufactured sintered members, the possibility is also provided in this known clutch for sintering to occur directly onto the counter rotor or the pressure plate, called support elements below, as a friction-lining layer. By sintering a friction-lining layer directly onto a metallic support element, the strength of the connection attained is more than enough at increased load requirements. For the application of a clutch described previously, the attainable strength is insufficient to transfer torque.
GB 1345847 discloses a process to manufacture friction members in which in general a powdered sinter material is sintered with a powdered layer of copper on a support element.
The object of this invention is to create a process that enables the connection of a powder-metallurgically sintered member solidly to a metallic support element.
In an especially advantageous configuration of the invention, it is provided that, for the green body, a basically copper-free sintered powder is provided. Here it is appropriate if the green body is basically composed of a mixture of an iron powder and powder-like additives. A green body composed in this manner and a sintered body formed from it following sintering present the advantage that the sintered powder can be composed in relation to standards with regard to strength and additional standards for attaining special properties with a view toward the intended use, whereby the iron powder can also be an alloyed iron powder. Thus, for example, it is possible for sintered friction elements to add xe2x80x9cstop substancesxe2x80x9d as friction supports through appropriate hard material, as, for example, metal carbides or the like. In practice, it has surprisingly turned out that a friction element made of a copper-free sintered element (which has been joined according to the invention with the support element during the sintering process in the manner of a hard solder, for example for an element in shiftable clutches) has a clearly better friction behavior than the friction elements manufactured according to the traditional procedure of a copper-containing iron sinter powder. This, according to previous information, is to be attributed to the fact that the copper body applied to the green body on copper-free sintered powder melts even before starting the sintering process and largely flows through the pores of the green body, and in penetrating the pore structure merely wets the free surface of the already sintered matrix of the sintered friction element so that, other than with a green body with admixed copper components in the metal powder, a better accuracy in size exists.
It is further provided in configuring the invention that basically pure copper is used in the copper element. In an advantageous further configuration of the invention, it is provided that an alloyed copper is used for the copper body. Preferably such metals are used as alloy components which bring about a wetting of the surface of the matrix of the sintered body basically formed by iron. The copper body can be comprised by a sheet of suitable metal or by a stamping of copper powder. With the use of such a stamping, there exists the possibility of admixing with the copper powder still further powder components, for example, an iron powder and a manganese powder or an iron powder alloyed with manganese so that the wetting capacity of the melts arising from the copper body is improved in relation to the surface of the matrix of the sintered body.
In configuring the invention, it is provided that the thickness of the copper body comes to at least 10% of the thickness of the green body. In configuring the invention, it is also provided that the copper content of the copper body comes to at least 20% by weight in relation to the weight of the green body. In proportioning the amount of copper, the porosity of the sintered body must also be taken into consideration, since sintered bodies with a larger pore volume hold part of the amount of copper in the pore structure, so that through a correspondingly greater amount of copper, the xe2x80x9cthrough flowxe2x80x9d up to the surface of the support element is guaranteed.